1. Field of Invention
The present invention relates to a bar-code, and more particularly to a two-dimensional bar code, a method for encoding data into a two-dimensional bar code symbol, and a method for decoding the two-dimensional bar code symbol into a predetermined set of data.
2. Description of Related Arts
A conventional two-dimensional bar code usually has three portions: characteristic pattern portion, format information portion and data codewords portion. The characteristic pattern portion directs image recognition algorithms to recognize and orient the bar code symbol. The format information portion stores some parameters related to the symbol format and data error correction. The data codewords portion stores data encoded after error correction. The bar code symbol cannot be recognized if its characteristic pattern portion and format information portion are damaged to some extent. In the bar code symbol these two portions are vulnerable areas that reduce the reliability of the two-dimensional bar code.
Referring to FIG. 1 of the drawings, a two dimensional bar code ‘PDF417’ is illustrated. Those bars and spaces of varying widths at both left and right ends of the symbol are its characteristic pattern portions 10, and the regions close to the characteristic pattern portions 10 are its format information portions 20. If the characteristic pattern portions 10 and the format information portions 20 are damaged to a certain extent, the symbol cannot be identified properly.
Referring to FIG. 2 of the drawings, another two-dimensional bar code ‘QR’ is illustrated. Its characteristic pattern portions 30 are at the top left corner, at the top right corner and at the bottom left corner. In the vicinity of the characteristic pattern portions 30, there are three small regions marked out with dashed lines which are the format information portions 40. If the characteristic pattern portions 30 and the format information portions 40 are damaged to a certain extent, the symbol cannot be recognized properly.
From past experience, one skilled in the art would obviously come to a conclusion that a major drawback of the above-mentioned conventional two-dimensional bar codes is that their characteristic pattern portion and format information portion are incapable of distinctively and individually identifiable, vulnerable and generally have little resistance of anti-deformation.